Pressure-flow behavior during RIRS irrigation: a controlled ex vivo porcine kidney study of flow-dependent apparent outflow resistance.

Abstract

Purpose: To measure actual irrigation flow and intrarenal pressure (IRP) under different irrigation modes during retrograde intrarenal surgery (RIRS), and to develop a controlled ex vivo empirical pressure-flow model for the tested endoscope-sheath configurations.

Methods: A controlled ex vivo porcine kidney-ureter model was used, with all measurements taken using a 200 μm holmium laser fiber in the working channel of a 7.5Fr or 6.3Fr flexible ureteroscope and 10/12Fr or 12/14Fr suction access sheaths. Manual syringe, gravity, and automatic pump irrigation were tested across three porcine kidney-ureter units. Each condition was measured in triplicate (technical repeats); condition-level means were used for model fitting and internal assessment.

Results: Actual flow rose with driving pressure and fell with scope deflection. For the ZSR pump, flow increased from 32.0 to 99.8 mL/min (7.5Fr) and from 9.3 to 49.7 mL/min (6.3Fr) across the tested pressures. Pooling pump and syringe data, apparent outflow resistance increased at higher flow, so the non-suction relation was described by [Formula: see text]. Across 20 condition-level means, the complete model gave an RMSE of 1.04 mmHg and R² of 0.994. In a single-operator full-speed syringe test, back-calculated driving pressure was approximately 600 to 770 mmHg.

Conclusion: In this controlled ex vivo model, apparent outflow resistance was flow-dependent, and the empirical model described the tested pressure-flow behavior. Forceful syringe flushing should not be routine when controlled pump, water-injection, or adequate gravity irrigation is available. Clinical safety claims require in vivo and clinical validation.